Method and system for controlling access to a wireless communication medium

ABSTRACT

A method and apparatus may be used to broadcast a first beacon and a second beacon in a beacon interval. The first beacon may include an indicator that indicates whether a second beacon will be transmitted within the beacon interval. The first beacon may be a legacy beacon and the second beacon may be a non-legacy beacon. A legacy beacon may be decodable by any station (STA) and a non-legacy beacon may be decodable only by non-legacy STAs.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.11/199,446 filed Aug. 8, 2005, which issued on Feb. 11, 2014 as U.S.Pat. No. 8,649,322, which claims the benefit of U.S. Provisionalapplication No. 60/601,323 filed Aug. 12, 2004, the contents of whichare incorporated by reference.

FIELD OF INVENTION

The present invention is related to a wireless communication system.More particularly, the present invention is related to a method andsystem for controlling access to a medium in a wireless communicationsystem.

BACKGROUND

The IEEE 802.11 working group, Task Group n (TGn), has been set up todevelop a new wireless standard with a data rate in excess of 200 Mbpsto deliver high throughput data, such as high definition television(HDTV) and streaming video. The theoretical maximum throughput ofexisting standards IEEE 802.11a and IEEE 802.11g is around 54 Mbps, andthe highest usable throughput is around 25 Mbps.

It would be desirable to provide a more efficient medium access control(MAC) architecture and associated procedures which support a variety ofphysical layer interfaces that may be optimized to meet a throughput of100 Mbps on top of the service access point of the MAC layer under thecurrent IEEE 802.11 wireless local area network (WLAN) servicerequirements and deployment scenario assumptions.

SUMMARY

The present invention is related to a method and system for controllingaccess to a medium in a wireless communication system. A MACarchitecture builds upon the existing IEEE 802.11 MAC architecture andits IEEE 802.11e extensions to provide higher performance. A superframestructure is defined in time domain to include a contention free periodwhich has at least one scheduled resource allocation (SRA), at least onemanagement SRA (MSRA) and a contention period. An extended beacon (EB)including information about the SRA and MSRA is transmitted for. The MACarchitecture reduces station battery consumption, supports higherthroughput for non-real time (NRT) traffic and is more efficient forreal time (RT) traffic than IEEE 802.11e while maintaining fullcompatibility. The present invention reduces station (STA) batteryconsumption, supports higher throughput for non-real time (NRT) trafficand is more efficient for real time (RT) traffic than required by IEEE802.11e while maintaining full compatibility.

The present invention eliminates a hidden node problem. The presentinvention provides higher performance for NRT services, better stabilityand a higher number of users or a higher throughput than required byIEEE 802.11e on enhanced distributed channel access (EDCA) for NRTservices, such as a file transfer protocol (FTP) or web browsing undersimilar latency requirements, and corrects the IEEE 802.11e unfairnesstowards access point (AP) transmissions.

The present invention provides higher performance for RT services whileguaranteeing quality of service (QoS), reduced STA power consumption,higher MAC efficiency and throughput for all RT applications, lowerdelay jitter compared to IEEE 802.11e EDCA, higher MAC efficiency forvoice over Internet protocol (VoIP) applications with similar delayjitter compared to IEEE 802.11e hybrid coordination function (HCF)controlled channel access (HCCA).

The present invention provides backward compatibility with IEEE 802.11MAC and its IEEE 802.11e extensions, as well as with IEEE 802.11k.

The present invention supports efficient physical (PHY) operationthrough orderly back-and-forth transmissions that enable the timelyreception of channel quality information (CQI) used to determine codingand modulation rates, the use of channel reciprocity or, if necessary,reception of channel state information (CSI) which may be used tooptimize transmitter operation, support of hybrid automatic repeatrequest (ARQ), and enhanced frequency hopping (optional).

The present invention incorporates a flexible design which supportsdifferent types of PHY interfaces including, but not limited to,multiple input multiple output (MIMO) and forward error correction (FEC)coding techniques, orthogonal frequency division multiple access (OFDMA)operation, and both a 20 MHz and 40 MHz high throughput (HT) STA in thesame superframe, which is extendable to other bandwidths if necessary.

The present invention provides enhanced peer-to-peer direct transfer ofdata under the control of an AP and support of relay operation to extendservice area coverage and rates.

A method and apparatus may be used to broadcast a first beacon and asecond beacon in a beacon interval. The first beacon may include anindicator that indicates whether a second beacon will be transmittedwithin the beacon interval. The first beacon may be a legacy beacon andthe second beacon may be a non-legacy beacon. A legacy beacon may bedecodable by any station (STA) and a non-legacy beacon may be decodableonly by non-legacy STAs.

BRIEF DESCRIPTION OF THE DRAWINGS

A more detailed understanding of the invention may be had from thefollowing description of a preferred example, given by way of exampleand to be understood in conjunction with the accompanying drawingwherein:

FIG. 1 is a block diagram of MAC architecture in accordance with thepresent invention;

FIG. 2 is a block diagram of a superframe structure with legacyoperation in accordance with the present invention;

FIG. 3 is a block diagram of a superframe structure without legacyoperation in accordance with the present invention;

FIG. 4 is a block diagram illustrating a flexible superframe structurein accordance with the present invention;

FIG. 5 is a diagram illustrating slotted Aloha operation in MSRA;

FIGS. 6 and 7 are block diagrams of exemplary frame exchange sequenceswith and without ACK, respectively, in accordance with the presentinvention;

FIG. 8 is a diagram of beacon and EB transmission in accordance with thepresent invention;

FIG. 9 is a block diagram of an IE for frequency hopping in accordancewith the present invention;

FIG. 10 is a block diagram of a resource allocation request (RAR) framein accordance with the present invention;

FIG. 11 is a block diagram of a frame body of the RAR frame inaccordance with the present invention;

FIG. 12 is a block diagram of each RAR block in accordance with thepresent invention;

FIG. 13 is a block diagram of a resource allocation response frame inaccordance with the present invention;

FIG. 14 is a block diagram of a frame body of the resource allocationresponse frame in accordance with the present invention;

FIG. 15 is a block diagram of a general management frame in accordancewith the present invention;

FIG. 16 is a block diagram of a frame body of the management frame inaccordance with the present invention;

FIG. 17 is a block diagram of an OFDM MIMO Parameter Set element inaccordance with the present invention;

FIG. 18 is a block diagram of a CP Access element in accordance with thepresent invention;

FIG. 19 is a block diagram of an EB element in accordance with thepresent invention;

FIG. 20 is a block diagram of an SRA Schedule element in accordance withthe present invention;

FIG. 21 is a block diagram of an SRA Block IE in accordance with thepresent invention;

FIG. 22 is a block diagram of an MSRA schedule element in accordancewith the present invention;

FIG. 23 is a block diagram of an MSRA Block element in accordance withthe present invention;

FIG. 24 is a block diagram of an ORA Schedule element in accordance withthe present invention;

FIG. 25 is a block diagram of each ORA Block IE in accordance with thepresent invention;

FIG. 26 is a block diagram of an RAR Specification IE in accordance withthe present invention;

FIG. 27 is a block diagram of a Resource Allocation Notification IE inaccordance with the present invention;

FIG. 28 is a block diagram of a superframe structure for simulation;

FIG. 29 is a diagram of simulation results for throughput comparison;

FIG. 30 is a diagram of simulation results for average delay;

FIG. 31 is a diagram of simulation results for average delay vs.application data rate for eight (8) users;

FIG. 32 is a diagram of simulation results for average system throughputvs. application data rate for eight (8) users;

FIG. 33 is a block diagram of direct link protocol (DLP) signaling inaccordance with the present invention;

FIG. 34 is a block diagram illustrating message exchange for DLP setupin accordance with the present invention;

FIG. 35 is a diagram showing slotted Aloha operation with collective ACKin MRAP in accordance with the present invention;

FIG. 36 is a diagram showing slotted Aloha operation with immediate ACKin MRAP in accordance with the present invention;

FIG. 37 is a flow diagram of a process for SRA assignment in accordancewith the present invention; and

FIG. 38 shows a wireless communication system including an AP and a STAin accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereafter, the terminology “STA” includes but is not limited to a userequipment, a wireless transmit/receive unit (WTRU), a fixed or mobilesubscriber unit, a pager, or any other type of device capable ofoperating in a wireless environment. When referred to hereafter, theterminology “AP” includes but is not limited to a base station, aNode-B, a site controller or any other type of interfacing device in awireless environment. Hereafter, the terminology “STA” refers to a STAconfigured to support IEEE 802.11n and the terminology “legacy STA”refers to a STA configured to support IEEE 802.11 or IEEE 802.11e.

Hereinafter following terminology will be used in the present invention.AP means any AP that is compliant with the proposed IEEE 802.11nstandard. STA, (or interchangeably IEEE 802.11n STA, high throughput(HT) STA), means any STA that is compliant with the proposed IEEE802.11n standard. Legacy AP means any AP that is complaint with IEEE802.11 standards predating the IEEE 802.11n standard and therefore doesnot support the proposed IEEE 802.11n standard. Legacy STA includes anySTA that is complaint with IEEE 802.11 standards predating the proposedIEEE 802.11n standard and therefore does not support the proposed IEEE802.11n standard.

Hereafter, the present invention will be described in context with anIEEE 802.11n environment. However, it should be noted that the presentinvention is applicable to any other wireless communicationenvironments.

The MAC in accordance with the present invention builds upon theexisting IEEE 802.11 MAC architecture and its IEEE 802.11e extensions toprovide higher performance for networks which include IEEE 802.11ncompliant AP and STAs. The system in accordance with the presentinvention reduces station battery consumption, supports higherthroughput for NRT traffic and is more efficient for RT traffic thanIEEE 802.11e while maintaining full compatibility, supporting bothlegacy and high throughput STA at the same time. The present inventionprovides MAC architecture and procedures supporting a variety ofphysical layer interfaces that may be optimized under the current IEEE802.11 WLAN service requirements and deployment scenario assumptions.

In order to achieve uninterrupted operation for STA while maintainingfull backward compatibility, a superframe is partitioned between HTperiod(s) used for IEEE 802.11n access and an optional legacy periodused for IEEE 802.11 and IEEE 802.11e access. Both RT and NRT servicesare provided to STA during the IEEE 802.11n period of the super frameusing different methods. NRT operation is typified by unpredictable andwidely varying data rates with no formal latency requirements.

Downlink (AP→STA) data transfers are done at the discretion of thecontroller, which will generally (but not necessarily) be implemented inthe AP. No contention can happen during this time, either from legacy orHT STA. Acknowledgement and feedback packets are regularly transmittedin the reverse direction (uplink, or STA→AP) after single or multiplepackets, depending on conditions and as has been negotiated between thenodes and can be exploited to optimize physical layer performance. Themechanism is flexible enough to allow the use of sophisticatedscheduling algorithms which may take into account buffer occupancy aswell as channel conditions to further enhance system performance. Thisoperation takes place during Scheduled Resource Allocation (SRA) periodsin the superframe.

Uplink (STA→AP) data transfers are accomplished via a slotted Alohabandwidth request, shortly after followed by a response indicatingpermission to transmit data. As for the downlink case, acknowledgementand feedback packets are regularly transmitted in the reverse directionafter single or multiple packets, depending on conditions and as hasbeen negotiated between the nodes. The requests are sent during amanagement SRA (MSRA) while data transfers are performed during an SRA.The usage of short packets in a slotted Aloha mode increases throughputand stability at high loads and eliminates the hidden node problem asSTAs are not required to sense the medium for contention. As in the caseof the downlink, the mechanism is flexible enough to allow the use ofsophisticated scheduling algorithms which may take into account bufferoccupancy as well as channel conditions to further enhance systemperformance. Small packets used for management and control purposes,(e.g. in order to set up RT operation), may also be exchanged at thistime.

RT operation is typified by predictable data rates. The resources areindicated to each user by an extended beacon (EB) transmitted once orseveral times per superframe. As a result, the polling overhead isreduced, but more importantly STAs are required to listen only a smallfraction of the time which reduces the STA power consumptionrequirements. As in the case of NRT services, acknowledgement andfeedback packets are regularly transmitted in the reverse directionafter single or multiple packets, and can be exploited to optimizephysical layer performance. As for NRT scheduling can consider bothtraffic and channel conditions.

The EB has the several applications in the IEEE 802.11k standard. First,the EB allows power saving when an STA scans frequency bands to searchfor neighbors. Second, the EB allows for reduction of interruption timeduring neighbor scanning for BSS transition. Third, the EB extends therange of the STA.

The EB can be transmitted at a low rate or high rate. At the low rate,the EB has applications in extending range. At high rates, the EB hasapplications in decreasing beacon overhead. The EB is applicable toseveral scenarios including IEEE 802.11n and non-IEEE 802.11n, 10/20/40MHz and dual 20 MHz operation (IEEE 802.11n).

The EB can replace the standard beacon and will then contain some or allthe information elements of the standard beacon. Also, the EBs are ofvariable length.

FIG. 1 is a block diagram of a MAC architecture 100 which expands thearchitecture adopted for IEEE 802.11e in accordance with the presentinvention. The MAC architecture 100 includes a resource coordinationfunction (RFC) 105 and a distributed coordination function (DCF) 110.The RCF 105 may include a point coordination function (PCF) 115, anenhanced distributed channel access (EDCA) 120, a hybrid coordinationfunction (HCF) controlled channel access (HCCA) 125, an RCF managementchannel access (RMCA) 130 and an RCF scheduled channel access (RSCA)135. The RMCA 130 and the RSCA 135 are new functions added for IEEE802.11n. The RCF 105 and the DFC 110 are present with HCF and PCF forbackward compatibility.

The RCF 105 is usable only in IEEE 802.11n configurations and providesfull quality of service (QoS). All IEEE 802.11n STAs implement the RCF105. The RCF 105 uses functions from the DCF 110 and new schedulingfunctions to allow a set of frame exchange sequences for data transferswith or without QoS. There are two access procedures supported by theRCF 105 for management and scheduling functions. First, RMCA 130 isprovided by the RCF 105 for small packet transfers and schedulerequests/reservations. Second, RSCA 135 is provided for contention freedata transfer providing full QoS support. Typically, the RMCA 130 isused for all bandwidth requests for services which will be supported bythe RSCA 135.

The superframe structure used when the RCF 130 is in operation isdescribed hereinafter. FIG. 2 is a block diagram of a superframestructure 200 with legacy operation in accordance with the presentinvention. A superframe 205 comprises a legacy beacon 210, a legacycontention free period (CFP) 215 and a legacy contention period (CP)220. An IEEE 802.11n period 225 is defined in the CFP 215. The IEEE802.11n period 225 contains contention as well as scheduledtransmissions for IEEE 802.11n STAs. The CFP 215 ensures that legacySTAs will not access the channel unless polled by the AP. When an RCF105 is operating in a basic service set (BSS), a CFP 215 and a CP 220are generated based on the need to support legacy STAs and IEEE 802.11nSTAs.

The IEEE 802.11n STAs are supported in a period defined as IEEE 802.11nperiod 225. The CP is used to support operation of legacy STAs. IEEE802.11n STAs are permitted to contend here though it may not be thepreferred mode of operation. The IEEE 802.11n period 225 supports EBs,scheduled resource allocations (SRAs) and management SRAs (MSRAs) withvariable guard times separating them. When legacy operation is notenabled, the superframe structure 200 does not contain the beacon 210and CP 220.

A simple superframe structure 300 where the SRAs are allocated basedonly on time is shown in FIG. 3 when legacy operation is disabled. Thesuperframe structure 300 is independent of the physical (PHY) layer andsupports all types of PHY layers. In the case where the PHY layer allowsallocation of variable subchannels (such as in OFDMA) the superframewould be as shown in FIG. 4.

The AP gains control of the wireless medium for the CFP 215 by includinga contention free (CF) parameter set element in the Beacon frames. Thus,all STAs set their network allocation vectors (NAVs) to the“CFPDurRemaining” value in the CF parameter set element, which indicateshow much longer the CFP will last. This prevents contention in the CFP215 by the legacy STAs. The CFP 215 generated by the AP always ends witha CF-End frame. The IEEE 802.11n period may be established anywhere inthe CFP 215 by the AP.

The legacy beacon 210 is transmitted in the 20 MHz channel so that allSTAs including IEEE 802.11n STAs can receive it. It contains all of thelegacy information and is modified to include the information about theEB in the IEEE 802.11n period. The periodicity, frequency band, andsubchannel information about the EB is explicitly included in thebeacon. The EB includes information on the locations, durations andtypes of the SRAs, MSRAs and open RA (ORA) periods, in addition to thesystem information defined in the current IEEE 802.11 beacon.

The EB may be transmitted at a higher data rate than the beacon. Whenlegacy operation is enabled the first occurrence of the EB isimmediately following the beacon. The subsequent occurrences of the EBare based on the periodicity of the EB.

In the absence of legacy operation, legacy beacon need not be present,and the EB operates as an only beacon in the system. In the presence oflegacy operation, a superframe is defined as a period between two legacybeacons. Otherwise, it is a period between two EBs. There can be one ormore EBs in a superframe in presence of a legacy beacon. IEEE 802.11nSTAs may listen to the beacon to locate the EB(s) or they may directlylisten to the EB(s). The length of EB is variable.

The STAs can access the wireless medium in an efficient way when2809577-1 compared to legacy STAs to transmit MAC protocol data units(PDUs), (i.e., MPDUs). The basic unit of allocation to an STA under theRCF 105 is an SRA. Each SRA is defined by a starting time and duration.An SRA is assigned to an STA by the RCF 105 in the IEEE 802.11n periodunder RSCA 135. The assignment of the SRA may be set up by an STA makinga request under the RMCA 130. The transmissions do not extend beyond theassigned SRA. During the specified duration of an SRA assigned to anSTA, no other STA can compete for the wireless medium.

MSRAs are management SRAs set up by the RCF 105 in the IEEE 802.11nperiod 225 under the RMCA 135. MSRAs are used for management functionssuch as resource request and response, association request and response,and exchange of management information. Each MSRA has a starting timeand duration. Transmissions shall not extend beyond the duration of anMSRA. The RCF shall ensure that sufficient MSRAs are allocated in eachIEEE 802.11n period. STAs compete for the wireless medium during MSRAs.

ORAs are the resources that are available after all the SRAs and MSRAshave been allocated in the superframe. It can also arise because an SRAhas not been fully utilized. It is different from SRAs as SRAs areallocated to a given traffic stream of an STA. These resources arecontrolled by the AP. It can be used by the AP for downlink and uplinktransmission of NRT services and control traffic; to providesupplemental SRAs; and for broadcast and multicast traffic. Some ORAscan be assigned to a group of STAs.

The RMCA mechanism provides access to the wireless medium for managementfunctions within IEEE 802.11n period by setting up MSRAs for data packetexchanges and request/reservation for scheduled transmissions.

The channel access procedure under RMCA depends on the type of MSRA thatis operational. The AP announces the RMCA parameters in the EB. Theseparameters include information about the MSRAs such as location,duration, and access mechanism and optionally type. The type coulddifferentiate between MSRAs used for associated and un-associated STAs.Preferably, a slotted Aloha contention based access mechanism is used inall MSRA. However, a CSMA/CA mechanism as defined by IEEE 802.11e or anyother contention mechanisms may be implemented. The contention mechanismis signaled in the EB.

MSRAs allow associated and unassociated STAs and AP to exchange messagesin a contention mode. The data exchange is typically small data packets,such as resource allocation requests for scheduled transmissions,association/reassociation requests. The data transmitted by associatedSTAs are typically Resource Allocation Request frames in order torequest assignment of SRAs in the IEEE 802.11n period. The datatransmitted by new or unassociated STAs are typicallyAssociation/Reassociation Request frames in order to request associationwith APs. In addition, small packets may optionally be transmitted bySTAs subject to a certain limit in the size of the packet. The MSRA isidentified for at least one of data packet and control packettransmission.

FIG. 5 shows a slotted Aloha mechanism 500 for an MSRA 505. In theslotted Aloha mechanism 500, STAs access the wireless medium with shortdata packets. The wireless medium is divided into time slots 510 of sizeequal to the data packet duration, and transmissions are allowed only atthe beginning of the slots.

An exponential backoff mechanism is implemented as follows. A back offcounter is maintained at each STA and is decremented every slot. Apending packet is transmitted when the back off counter becomes zero.The back off counter is chosen as a uniformly distributed randomvariable from a contention window (CW). In the first attempt, the CW isset to a minimum. The size of the CW grows with the number ofretransmission attempts until it reaches an upper limit. The rate atwhich the CW grows may optionally depend on the priority of the traffic.For example the smaller the access delay specification of the trafficthe slower the growth of the CW. Controlling the CW based on the accessdelay specification will allow better management of access delays in aslotted Aloha access under high load situations. At the end of the MSRA,the AP transmits a collective response Frame 515, which is a collectiveresponse for all STAs that contended in the MSRA 505. The collectiveresponse frame 515 includes resource allocation responses for associatedSTAs that successfully transmitted their resource allocation requests,and association/reassociation responses for unassociated STAs thatsuccessfully transmitted their association/reassociation requests. TheSTAs that were unsuccessful have to retransmit their packets using theback off counter. The backoff counter is decremented only during MSRAperiods.

The Aloha mechanism 500 allows the RCF 105 to take into considerationmultiple factors regarding the service requirements, buffer occupancyand channel conditions of each of the STAs that has requested resources.

If a CSMA/CA scheme is used for MSRAs, each successful transmission froman STA is individually acknowledged with an ACK message from the AP.This is inefficient when compared to the collective response in the caseof the slotted Aloha mechanism 500 described above.

The RSCA 135 uses a resource coordinator (RC) that provides QoS servicesupport through scheduled resource allocation. The RC operates underrules that are different from the point coordinator (PC) and the hybridcoordinator (HC).

SRAs are assigned to STAs to serve all types of traffic, (e.g. NRT andRT). The RC can serve traffic with SRAs that change little acrosssuperframes and would be recurring until the transmission is terminatedby the originating STA. Such SRAs, (that are quasi-static in nature),are suitable for RT periodic traffic. However, the RC can also servetraffic with SRAs that may change frequently from superframe tosuperframe and spanning one or more superframes to transmit a databurst. These types of SRAs, (that are dynamic in nature), may be used toserve any type of traffic and are allocated per data burst. Thismechanism allows the RC the flexibility to rearrange SRA assignments tooptimize the utilization of resources. The RC shall account for alltransmissions, including the response frames that will be part of theSRA transmission when setting the SRA duration in an assignment of anSRA to an STA. All resources not assigned as SRAs or MSRAs are managedby the RC as ORA. ORAs have many applications and allow the RC toefficiently utilize resources that are not scheduled.

Non-AP STAs may send resource allocation requests during MSRAs whileproviding QoS information in the Resource Allocation RequestSpecification information element (IE), directed to the RC. STAs shouldindicate that the transmission should take place only under RSCA andalso optionally under RMCA.

The RC traffic delivery and SRA assignment are scheduled during the IEEE802.11n period to meet the QoS requirements of a given traffic. The APannounces the parameters for the assigned SRAs in the EB. An STA mayinitiate multiple frame exchange sequences during an SRA of sufficientduration to perform more than one such sequence. SRA assignments may bebased on the RC's BSS-wide knowledge of pending traffic belonging tousers with different traffic characteristics and is subject to theBSS-specific QoS policies.

The SRA assignment and modification involves the creation, modification,and termination of SRAs for the exchange of data between two or moreSTAs. An STA may support one or more connections depending upon theapplications it supports. An SRA assignment to an STA for a connectionto serve a given type of traffic involves creation of SRA allocationsover one or more superframes. The assignment may be modified as requiredduring the lifetime of connection. Creation, modifications, andterminations of SRAs between two or more STAs are carried out bynegotiations between the originating STA and the AP using the ResourceAllocation Request and Resource Allocation Response messages. Once anSRA is assigned with an index, the SRA may be modified or terminated.Only an STA that is associated with an AP shall send a ResourceAllocation Request message to the AP for an SRA assignment.

The access delay for an SRA can be managed by including a priority foraccess in MSRAs. Once access is granted there is a guaranteed access tothe wireless medium/channel with the required QoS.

For the creation of an SRA, the originating STA sends a ResourceAllocation Request to the AP for a new connection with target STAs in anMSRA, and sets the destination address list to the target STA addresses,Resource Index to a default value indicating unassigned status, RAR IDto a unique value for the duration of the negotiation, RAR Type toquasi-static assignment or dynamic assignment, and all other parametersto appropriate values.

The AP on receiving the Resource Allocation Request message from theoriginating STA shall respond with a Resource Allocation Responsemessage to the originating STA in an MSRA with the Resource Index fieldset to an unused value and all other parameters to appropriate values.Service Duration per Superframe and Service Interval determine theduration of a quasi-static SRA assignment and its frequency with respectto the superframe in a recurring fashion. Service Duration perSuperframe, Service Interval, and Maximum service duration determine theduration of a dynamic SRA assignment, its frequency with respect to theSuperframe, and service duration for the data burst.

The AP may then update the EB with the newly assigned SRA. The AP shallannounce in the EB and the Resource Allocation Response (collectively orindividually) the creation of all SRAs. It shall also announce thecreation of connections for the destination STAs.

The modification of an assigned SRA may be achieved by sending aResource Allocation Request message to the AP with Resource Index fieldset to the assigned value and all other fields modified as desired. Thiscan be done in three ways. Firstly the modification can be carried outusing an MSRA. Secondly the Resource Allocation Request message may bepiggybacked on data within an SRA. The corresponding response may bepiggybacked on data from AP in the SRA and would take effect in the nextsuperframe. Another method would be to support this message exchange inan ORA.

The termination of an assigned SRA may be achieved by sending a ResourceAllocation Request message to the AP with Resource Index field set tothe assigned value and all other fields set to null or zero. Only theoriginating STA may terminate an established SRA.

A supplemental SRA is a one time allocation that may be set up byincluding the setup information in the header of the last messagetransmission from the AP to the STA in the given SRA. For a downlinktraffic stream, the AP can piggyback the resource allocation informationon the data packet. For uplink, the AP may piggyback this supplementalSRA information on a data packet. Supplemental SRA information may beactual allocation information or an indication to listen in certain ORA.

SRA locations in the IEEE 802.11n period of the superframe are specifiedin the EB. SRA location information can be modified after N EBs. Thenumber N can be based on at least one of the application and systemrequirements. This reduces the overhead in EB. In the presence of legacyCP, the information must be sent every EB. This is to ensure that legacybeacon drift can be handled by the EB.

In an assigned SRA the originating STA may initiate transmissions of oneor more frame exchange sequences, with all such sequences and frameswithin sequences separated by a short interframe space (SIFS) intervalfor continuous packet transmission or by other defined intervals betweena packet and an ACK. An STA may only send PHY layer information if ithas no data to sent. The AP can use it to learn channel stateinformation between the AP and the STA. FIGS. 6 and 7 are block diagramsof frame exchange sequence examples with or without ACK, respectively,in accordance with the present invention.

The RC shall ensure that the duration of any assigned SRA meets thestandard requirements of maximum contention free duration(dot11CFPMaxDuration) and maximum dwell time (dot11MaxDwellTime) so thatnon-AP STAs may use the assigned SRA without checking for theseconstraints. Within these limitations, all decisions regarding whatMSDUs and/or MPDUs are transmitted during any given SRA are made by theSTA that has been assigned the SRA.

During its assigned SRA when the STA receives a frame addressed to itand requires an acknowledgement, it shall respond with anacknowledgement (ACK) independent of its NAV. During an SRA assigned tothe STA, the STA can initiate a frame exchange sequence independent ofits NAV.

Any unused portion of an assigned SRA is returned to the RC. If an STAhas no traffic to send in the SRA assigned to it, or if the MSDU is toolong to send within the assigned SRA, the STA shall send an end oftransmission indicator. If there is no transmission in an assigned SRAfrom the corresponding STA, the AP grabs the wireless medium after a DCFinterframe space (DIFS) period (greater than SIFS period) and uses it asan ORA.

ORA allows a non-contention based access during which associated STAsmay exchange data packets with the AP. It is typically set up by the APin otherwise unassigned portions of the superframe or even in unusedSRAs. The AP coordinates the data exchange during ORA in both downlinkand uplink directions. In the uplink direction, the AP achieves this byassigning transmit opportunities to STAs. The contents of the packetsexchanged can be control packets or data packets. The transmissions canbe unicast, multicast or broadcast transmissions.

ORA can be assigned to a set of Connection IDs and/or STAs. Thisinformation is sent in the EB. The AP controls the data transmission andreception during this mode.

Some applications for ORA are as follows: An AP may send data packets toany STA and the STA may respond with a data packet or ACK. Toparticipate in an ORA, the STA should listen during the ORA. The AP maybroadcast or multicast messages or may multiplex different STAs. TheSTAs that are serviced in the ORA will be defined in an EB. The AP cansend an aggregated downlink transmission to one or more STAs. The STAmay receive control information from the AP or may send controlinformation such as channel feedback

An SRA assignment is used to transmit one or more frame exchangesequences with the only restriction that that the final sequence shallnot exceed the SRA duration limit. RMCA shall not be used to transmitMSDUs belonging to an established traffic stream (after being acceptedby the RC for scheduling and assignment of SRAs) unless it is permittedto do so by appropriate setting of the Access Policy subfield of the TSInfo field in the resource allocation notification IE.

The superframe structure from the legacy MAC has been retained in theMAC of the present invention. Especially, in the presence of legacyservice there is a beacon, CFP and CP as in legacy. When legacy supportis not enabled, the beacon, CP, and any legacy support in the CFP becomeoptional.

Comparison with Legacy Functions.

The RC frame exchange sequences can be used among STAs mainly in theIEEE 802.11n period within the CFP (as in PC used in PCF). However, itdiffers from PC and HC in several ways although it may optionallyimplement the functionality of a PC or HC. The most significantdifference is that the RC assigns SRAs of a specified duration to non-APSTAs and also MSRAs of various types for management functions.

The RC may also operate as a PC providing CF-Polls and/or a HC providingQoS(+)CF-Polls to associated CF-Pollable STAs using the frame formats,frame exchange sequences, and other applicable rules for PCF and HCF

Signaling and features of MAC to support various types of physical layeris explained hereinafter.

The MAC supports measurement frames for various physical layer needs,including received field strength, interference levels, channelinformation and transmitter calibration. The AP can instruct the STA tomeasure interference, received receive strength signal indicator (RSSI)(from other APs) in a particular channel (can be other than the channelof the AP). The AP can send signals for path loss measurement. Thetransmitted packet will contain the transmitted power whereas theresponse frame will contain the received power. These measurements arescheduled in ORA to send and receive small calibration frames. Physicallayer or another mechanism, implemented in the AP or elsewhere, mayindicate via some interlayer messaging to MAC the type and number ofmeasurements required.

For AP transmitter calibration, the AP may use STAs to aid in it'scalibration. A STA in turn sends a request in open MRA for its transmitantenna calibration. The AP let it calibrate its transmitter in regularMRA and/or open MRA. Typical fields in the packet sent for calibrationare measurement type set as TX calibration and the STA ID. The responsecontains RSSI information for every measurement request for a non-MIMOstation and channel parameters for MIMO capable STA.

Support for beam steering devices is provided as follows: The AP or STAcan indicate that they are in a beam steering mode. Special packets canbe used for picking the correct beam similar to the measurement signalsfor antenna calibration.

The AP is allowed to send the timing information back to the STA. An APcan detect the timing information from the offset from slotted Alohaslots. This information may be useful for OFDMA or 20 MHz/40 MHz system.

The AP and STA may contain certain physical characteristic or the bitsthat can be used to indicate and distinguish AP from STA.

The information regarding the MIMO capability of the AP may be sent asadditional fields in the legacy beacon (where such information is notnecessary for its decoding). MIMO capability parameters may be sent asphysical layer quantities on the EB. Other parameters may be sent as EBMAC information which may contain an indication whether or not the AP isMIMO capable and the details of the MIMO capability. STAs send theirMIMO capability information in the association message.

A MAC header contains optional IE about channel feedback informationsuch as channel quality and channel state. This information may be sentas a separate packet or piggybacked on a data packet and/or IEEE 802.11ACK packets. Optionally, some of these parameters may be sent asphysical layer information.

The HARQ capabilities are exchanged during association request andresponse. However, the HARQ may only be setup for certain application orchannel type. Hence, it can be piggy backed on the BW request packet andresponse. Packets are provided to initiate HARQ in the middle of anapplication. This is done to follow the philosophy used for Block ACK incurrent IEEE 802.11e standard.

HARQ feedback information can be sent as a separate packet orpiggybacked on a data packet. Some information although generated andreceived by the MAC may be better protected than user data (for example,using better coding or lower order modulation) or may be separatelycoded and interleaved.

Resources (i.e. time and/or frequency) are assigned to a user or a setof different users. A channel may be assigned for few milliseconds afterevery few 10's or 100's of milliseconds based on latency requirement ofthe application. Also, in the case of background application (NRTtraffic), the channels are assigned based on the availability. Theresources will not be assigned continuously over the duration of theapplication for any OFDM based IEEE 802.11 systems. However, the channelestimation is required for MIMO to operate efficiently.

An AP (or a STA) sends a PHY layer SYNCH and Preamble for channelinformation. There is no need to send the MAC packet as the resource isspecifically assigned to a STA or set of STAs. If the resources areassigned to more than one STA, the STAs do not send the PHY layerinformation for channel estimation. The details can be negotiated duringthe resource allocation request and response. A PHY header can use oneof the reserved bits to indicate that there is no MAC packet followingthe PHY.

An STA can listen to the packet before its scheduled time to get thechannel estimation information from the packets sent to other STAs. Thiswould require decoding source address information from the MAC header.It can also be done if the PHY header has some identification that thetransmission is from the AP.

An AP may need to support 20 MHz Legacy, 20 MHz IEEE 802.11n and 40 MHzIEEE 802.11n devices. FIG. 8 is a diagram for beacon and EB transmissionin accordance with the present invention. An AP sends an EB in both ofthe adjacent 20 MHz bands. The EB can be sent at the same time orstaggered over time. However, the resource allocation information may bedifferent in the two beacons depending on 20 MHz or 40 MHz operation.

Each device listens to the beacon in its own 20 MHz band. The EB informsthem of the details of scheduled transmissions and contention period.The AP may need to some smart scheduling to support two 20 MHz device indifferent bands at the same time. In order to avoid interference fromthe two adjacent 20 MHz band, the AP may have to ensure transmit andreceive to/from the two STAs should happen at the same time. Optional IEin MAC header of all the frames is provided to schedule the ACKtransmissions at a given time (instead of sending IEEE 802.11 ACK withinSIFs time).

Each device listens to any of the 20 MHz EB. Both the EBs send the sameinformation for 40 MHz device about their scheduled transmission and/orcontention period.

IEEE 802.11 standards have defined a frequency hopping (FH) system. TheFH Parameter Set defined in Beacon element contains the set ofparameters necessary to allow synchronization for STAs using a FH PHY.The information sent in the Beacon is shown in FIG. 9. The informationfield contains Dwell Time, Hop Set, Hop Pattern, and Hop Indexparameters. There are 3 hopping sequence sets with 79 hop patterns and77 hop index (divided among the 3 hopping sequence set). The FH dwelltime is decided by the MAC. The recommended dwell time is 19 time slots(around 20 msec).

Beacon contains the information of its own hopping between thenon-overlapping or overlapping frequency of 20 MHz BW. This may requirethat the Beacon be sent more frequently on all the frequencies. This isdifferent than what is in the standards. Each channel has 1 MHz bandseparated from the other channel by 1 MHz. The frequency hoppinginformation is sent during association or resource allocation responseto STAs. The hopping pattern may apply to any STA to AP or STA to STAdata exchange. With this scheme, the frequency is optionally changedonly for some STA instead of continuously frequency hopping, and rapidhopping improves QoS when latency requirements are tight.

In accordance with the present invention, the MAC optionally supportspacket forwarding. One or several nodes may forward the packet. Theconcept of forwarding can be useful for MESH networks or improving thepacket error rate (PER) for the destination node. In addition totraditional mesh techniques where the destination node receives therelay packet, a mode is allowed in which the destination node gets morethan one copy of the same packet.

In the current IEEE 802.11 system, a packet can have more than onedestination address. Forwarding for IEEE 802.11n can be enabled by thefollowing methods:

-   -   1) When To DS and From DS fields are not both ‘1’ then the        currently unused Address 4 field in the MAC header may be used        for the intermediate address in packet forwarding.    -   2) An information bitmap may be added to indicate the address of        destination and forwarding node. Forwarding node sends the        packet again.    -   3) A packet may have more than one destination address while not        being indicated as a multicast packet. In this case, there can        be pre-decided position for the destination node such as the        first or the last address in the address fields.

Resource allocation methods support allocating resources betweenforwarding node and destination node. This can be done by usingfollowing steps. Indication is made in the packet during resourceallocation that the traffic stream requires forwarding from anothernode. Information, (such as QOS, required data rate or the like), issent for setting up the resource between forwarding node and destinationnode. After resources have been set, the source node sends a packet. Thedesignated relay receives it and retransmits it after SIFS delay. Thepacket may optionally be re-coded before retransmission. The receivingnode returns an ACK after receiving the relayed packet. The ACK isreturned using the same mechanism or optionally directly not through therelay.

Frame formats. The frame formats that needs to be modified or added forthe IEEE 802.11n MAC layer is disclosed hereinafter.

In the Table 1, modified (in italics) and new frames are listedaccording to the type and subtype.

TABLE 1 Type value Type Subtype value b2 description b6 b6 b5 b4 Subtypedescription 00 Management 0000 Association Request 00 Management 0010Reassociation Request 00 Management 1000 Beacon 00 Management 1110Extended Beacon 00 Management 1111 Reserved 01 Control 0000-0011Reserved 01 Control 0110 Resource allocation request 01 Control 0111Resource allocation response

Note that even though some of the new frames are listed under controltype, they may as well be categorized as management type. They arecurrently listed under control type since there is only one moremanagement subtype value that is reserved.

Two control frames are added to support resource allocation request andresource allocation response for IEEE 802.11n STAs.

The RAR message is used to request, modify or terminate resourceallocation for all types of data, (i.e., NRT and RT). The RAR framestructure is shown in FIG. 10. The frame body of the RAR frame containsinformation is shown in FIG. 11. The length field corresponds to thelength of the RAR blocks to follow (there can be more than one from anSTA). Each RAR block has a structure as shown in FIG. 12. Number ofDestinations indicates the number of Receiving STAs (Unicast/Multicast)sought by the transmitting STA.

Destination Address list specifies the addresses of the receiving STAs.RAR ID is the identification number of the RAR. Resource index is anidentification number for a Resource Allocation. RAR Type indicateswhether the SRA is dynamic or quasi-static. RAR Specification is an IEspecifying the QoS requirement of the resource request.

The resource allocation response message is used to respond to RAR,modification or termination of resource allocation for all types ofdata. The frame structure is shown in FIG. 13. The frame body of theresource allocation response message is shown in FIG. 14. The resourceallocation notification (RAN) IE contains information on the allocatedresource. There are two options. First, the resource allocation responseis a response to an individual resource allocation request which can bedone contiguously in time for several STAs thereby eliminating the guardtime overhead between two resource allocation responses. Second, it canalso be done as a bulk response (when the RA field is set to broadcast)to the STAs that made a resource allocation request. This is efficientin reducing overhead but incurs the cost of decreased reliability sincethere is no ACK for broadcast/multicast.

Management frames have a general format, which is shown in FIG. 15, withthe type subfield in the frame control field set to management.

When an SRA already allocated is freed up it may be assigned to anothertraffic stream.

The Association/Reassociation request messages are modified to includeMIMO capability, subcarriers for pilot tone pattern and Device Typeindicating power saving capability. This information can be accommodatedusing the reserved bits in the capability field of the existingAssociation/Reassociation request message. Reassociation can be to a newAP.

The beacon frame has the frame format of a management frame with subtypeset to Beacon in the frame control field. A pointer to the EB for IEEE802.11n STAs is added to the existing beacon. The frame body containsinformation as shown in Table 2 with the modification in bold font.

TABLE 2 Order Information Notes 1 Timestamp 2 Beacon interval 3Capability information 4 SSID 5 Supported rates 6 FH The FH ParameterSet IE is present within Beacon Parameter frames generated by STAs usingfrequency-hopping Set PHYs. 7 DS The DS Parameter Set IE is presentwithin Beacon Parameter frames generated by STAs using direct sequenceSet PHYs. 8 CF The CF Parameter Set IE is only present within ParameterBeacon frames generated by APs supporting a PCF. Set 9 IBSS The IBSSParameter Set IE is only present within Parameter Beacon framesgenerated by STAs in an IBSS. Set 10 TIM The TIM IE is only presentwithin Beacon frames generated by APs. 14 QBSS The QBSS Load IE is onlypresent within Beacon Load frames generated by QAPs. The QBSS Loadelement is present when dot11QoSOptionImplemented anddot11QBSSLoadImplemented are both true. 15 EDCA The EDCA Parameter SetIE is only present within Parameter Beacon frames generated by QAPs. TheEDCA Set Parameter Set element is present when dot11QoSOptionImplementedis true and the QoS Capability element is not present. 23 QoS The QoSCapability IE is only present within Capability Beacon frames generatedby QAPs. The QoS Capability element is present whendot11QoSOptionImplemented is true and EDCA Parameter Set element is notpresent. 50 Extended The Extended beacon IE is only present withinBeacon Beacon frames generated by APs supporting IEEE 802.11n.

The EB frame has the frame format of a management frame with subtype setto EB in the frame control field. The frame body contains informationshown in Table 3.

TABLE 3 Order Information Notes 1 Timestamp (Legacy Information) Timestamp is a Fixed field representing the value of TSF TIMER 2 SSID(Legacy Information) SSID IE indicates the identity of an ESS or IBSS 3Supported (Legacy Information: optional if beacon Rates present)Supported Rates IE specifies the rates in the Operational Rate Set 4 FH(Legacy Information: optional if beacon Parameter present)The FHParameter Set IE is present within Set Beacon frames generated by STAsusing frequency- hopping PHYs. 5 DS (Legacy Information: optional ifbeacon Parameter present)The DS Parameter Set IE is present within SetBeacon frames generated by STAs using direct sequence PHYs. 6 CF (LegacyInformation: optional if beacon Parameter present)The CF Parameter SetIE is only present Set within Beacon frames generated by APs supportinga PCF. 7 IBSS (Legacy Information: optional if beacon Parameterpresent)The IBSS Parameter Set IE is only present Set within Beaconframes generated by STAs in an IBSS. 8 TIM (Legacy Information: optionalif beacon present)The TIM IE is only present within Beacon framesgenerated by APs. 9 OFDM OFDM MIMO IE specifies OFDM MIMO PHY MIMOrelated information Parameter Set 10 CP Access CP Access IE specifiespermission and legacy PHY information for IEEE 802.11n STAs to contendin the legacy Contention Period 11 SRA SRA Schedule IE mainly specifiesthe SRA time Schedule schedule for the Superframe 12 MSRA MSRA ScheduleIE contains the MSRA schedule, Schedule MSRA Type and MSRA Type specificinformation for the Superframe 13 ORA ORA schedule IE contains the OpenSRA Schedule schedule for the superframe 14 Channel Current Channel ofAP Information 15 New STA True (default). AP can advertise that it isnot Allowed supporting any new STAs.

The management frames of subtype Action are used for measurement requestand response packets, QoS (IEEE 802.11e support), or the like in thecurrent IEEE 802.11h and IEEE 802.11e standard. The Action frames areused for antenna calibration, extended DLP messages, channel feedbackinformation, and HARQ setup.

Following action frames are added under the DLP category:

-   -   1.) DLP Discovery Request: QSTA sends the packet to AP to get        the MAC address of the device by sending application        requirements.    -   2.) DLP Discovery Response: AP responds back with MAC address of        the device.    -   3.) DLP Teardown by AP: Add Action field for DLP Teardown by the        AP. The frame has an information filed called timer. AP expects        that QSTA sends the DLP teardown message to QAP within that        time.    -   4.) DLP Measurement Request: Add action item value for DLP        Measurement Request from the QAP 3315 to the QSTA 3305. It        contains the capability information of QSTA 3310.    -   5.) DLP Measurement Response: Add action item value for DLP        Measurement Response from the QSTA 3305 to the QAP 3315. It        contains measurement information and the MAC address of the QSTA        3310.

DLP Request frame is modified to include additional element to sendoptimal PHY data rate and certain other channel characteristic betweentwo STAs.

A new category for starting HARQ process is created in the Action framesin accordance with the present invention. There are two types of actionfields, HARQ Request and HARQ Response. The details of the HARQparameter can be filled later based on the agreed upon parameter by thestandard. Some of the parameters include, but are not limited to,Resource ID, H-ARQ indication, H-AQR ACK delay, and scheme of coding andmodulation used. The initiating information can also be piggybacked inthe resource allocation and request packet.

A new category for measurements is created as follows.

1.) Initial Antenna Calibration.

In the measurement category, action fields are defined for antennacalibration request and response packet. The response packet may be sentinstead of the IEEE 802.11 ACK. The response packet contains RSSIinformation or channel state information.

2.) Beam Steering Measurements.

In the measurement category, action fields are defined for beam steeringcalibration request and response packet. The response packet may be sentinstead of the IEEE 802.11 ACK. The response packet contains RSSIinformation or channel state information. The action field may have asubfield about the indication of start and end of beam steering. Thiscan be used if the STA or AP wants to inform the other side of runningbeam steering by using actual data packets instead of beam steeringmeasurement packets.

3.) Timing Offset Message.

An AP can measure the timing offset of the STAs due to propagation delayin slotted Aloha period. AP will send the timing offset information tothe STA. It is used by the STA to adjust its time with respect to theEB.

4.) Measurement Information:

In the measurement category, action fields are defined for measurements.These fields indicate RSSI and Interference measurement request andResponse. They contain a subfield with channel identity.

Channel Information such as channel quality and channel state need to besend to the transmitter side at certain frequency. Also, HARQ ACKs needto be sent either synchronously or asynchronously based on the HARQsetup parameters. This information can be sent in the MAC header asoptional IE piggybacked over data or as a separate packet.

Management Frame Body Components.

Fixed Fields.

Timestamp of the EB (similar to that in the beacon) is included so thatSTAs have another opportunity to synchronize. It represents the value ofthe time synchronization function (TSF) timer.

IEs are variable length frame body components in the Management andControl frames. IEs have a general format, shown in FIG. 16, comprisinga 1 octet Element ID field, a 1 octet length field and a variable-lengthelement-specific information field.

The set of valid IEs to support the modifications and new additions toMAC frames is given in Table 4.

TABLE 4 Information element Frame SSID Beacon, Extended Beacon SupportedRates Beacon, Extended Beacon OFDM MIMO Parameter Set Extended Beacon CPAccess Extended Beacon Extended Beacon Beacon RA Schedule ExtendedBeacon MRA Schedule Extended Beacon Resource Allocation Request ResourceAllocation Request Specification Resource Allocation NotificationResource Allocation Response H-ARQ Bitmap Hybrid ARQ AcknowledgementResponse H-ARQ Request Control Hybrid ARQ Acknowledgement Initiation CQIControl Channel Information CSI Control Channel Information

The Service Set Identity (SSID) element and Supported Rates element arethe same as in the beacon.

OFDM MIMO Parameter Set element is shown in FIG. 17. OFDM Capabilityfield has OFDM PHY support information. MIMO Capability field hasinformation on support for MIMO. Subcarrier Map information specifiessubcarriers for pilot tones and association.

CP Access element is shown in FIG. 18. CP permission field indicateswhether or not a IEEE 802.11n STA can contend in the legacy contentionperiod. CP PHY information provides the legacy PHY information for usein preamble for backward compatibility.

The EB element, shown in FIG. 19, indicates information aboutperiodicity, frequency band, and subcarriers for the EBss.

The SRA Schedule element, shown in FIG. 20, contains information on,number of SRAs in the IEEE 802.11n period and with corresponding SRAblocks of information.

Each SRA Block IE corresponds to a scheduled resource allocation andspecifies the SRA with Resource index, time offset, STA address, andResource duration. It is defined as shown in FIG. 21.

The MSRA schedule element specifies the number of MSRAs in the IEEE802.11n period and with corresponding MSRA blocks of information. It isdefined as shown in FIG. 22. Each MSRA Block corresponds to a managementscheduled resource allocation and provides the MSRA identificationnumber, time offset, duration, type (Unassociated and/or Associated),BSSID, packet type (control or data), contention scheme (slotted Alohaor CSMA/CA) as shown in FIG. 23.

The ORA Schedule element contains information on, number of allocatedORAs in the IEEE 802.11n period and with corresponding ORA blocks ofinformation. It is defined as shown in FIG. 24.

Each ORA Block IE, which is shown in FIG. 25, corresponds to an openresource allocation and specifies the ORA with Resource index, timeoffset, STA address list, and Resource duration.

The RAR Specification IE includes the QoS parameters for the requestedresource allocation. It has a structure as shown in FIG. 26. The set ofparameters defined in the RAR specification IE are more extensive thanmay be used or needed; unused fields are set to null using a messagebitmap.

The RAR Type field determines the format of the RAR Specification fieldinformation element. If RAR Type is Quasi-static then the RARSpecification IE will include most of the fields. However, if RAR Typeis dynamic then the RAR Specification IE may have those fields that arenot used set to zero. TS Info field contains information on Traffic Type(NRT, RT), direction, MAC ACK policy, Access policy (RMCA and/or RSCA)or the like. Nominal MSDU size specifies nominal size in octets of thetraffic. Maximum MSDU size specifies maximum size in octets of thetraffic. Maximum Service Intervals is the maximum duration between twosuccessive service periods. Service start time indicates to the AP thetime when the STA would be ready to send frames. Minimum Data Rate isthe lowest data rate specified at the MAC SAP for transport of MSDUs forthis traffic. Mean Data Rate is the mean data rate specified at the MACSAP for transport of MSDUs for this traffic. Peak Data Rate is themaximum allowable data rate for the transfer of MSDUs. Maximum Burstsize specifies the maximum burst of the MSDUs that arrive at the MAC SAPat the peak data rate. Delay bound is the maximum time allowed for thetransport of an MSDU from arrival at local MAC sublayer and completionof successful transmission or retransmission to the destination. TheMinimum PHY rate specifies the desired minimum PHY rate for thistraffic. The Surplus Bandwidth Allowance indicates the excess allocationto account for retransmissions.

The Resource Allocation Notification IE includes the response for therequested resource allocation. It has a structure as shown in FIG. 27.RAR ID is the identification number for the RAR. Resource index is theidentification for the Resource Allocation. TS Info field containsinformation on MAC ACK policy, Access policy (RMCA and/or RSCA) or thelike. Service Start Times specifies the offsets for the beginning ofallocations (can be more than one for certain traffic types such asvoice) within a superframe. Service Duration per superframe is theallocated time in a superframe (Beacon Interval). Number of allocationsper Superframe is the number of equal allocations into which the serviceduration per superframe is divided. Maximum Service Duration specifiesthe allocation over several superframes. Resource Type indicates whetherthe allocation is Quasi-static or dynamic. EB listening periodicityspecifies how often the STA needs to list to the EB for timinginformation. The allocation code gives information on whether or not theallocation was successful and under what conditions.

The performance of MAC in accordance with the present invention iscompared with the current IEEE 802.11e MAC for NRT Applications. Most ofthe NRT applications such as Internet File transfer, web browsing andlocal file transfer or the like are considered background and Besteffort services. The resources will not be assigned continuously forthese applications either in IEEE 802.11e or in accordance with thepresent invention. The current IEEE 802.11e MAC provides AP and STA samepriority for Background and Best Effort services. It is well known thatthe downlink throughput at the AP is low compared to uplink throughputat the STAs in the IEEE 802.11e MAC. The present invention provides APwith higher priority to co-ordinate transmission and reception of datapacket. Although any simulations results for downlink throughput numbersare not provided, it is obvious that the MAC of the present inventionwill not be unfair to the downlink traffic. Also, the present inventionimproves the uplink throughput compared to IEEE 802.11e. IEEE 802.11eand the present invention are simulated for bursty uplink traffic.

In the simulation a specific packet error rate is assumed. Differenterror rates apply to data packets and ACK packets, due to theirdifferent sizes. Moreover, for the MAC of the present invention, adifferent error rate applies to the reservation packets transmitted inthe Aloha part.

In the simulation certain percentage of hidden links is assumed. Link isdefined as the path between two STAs. For example, in a system with 12users there are 66 links, and 7 links are assumed to be hidden. For thecase of 4 users, there are 6 links, and one link is assumed to behidden.

The packet generation follows a Poison process. The mean is chosen sothat it yields the desired application data rate. TCP between thetraffic generator and the MAC have not been simulated. However, theassumption of exponential inter-arrival times provides burstiness in theNRT data packet generation.

The load is increased in the system by two different methods. In onemethod, the number of users is kept constant. But, the average data rateis increased for each user until the system becomes unstable. In theother method, data rate is kept constant, but the number of users isincreased until the systems become unstable.

The details of IEEE 802.11e is out of scope of this invention. Thesimulator has all the required IEEE 802.11e MAC functionalities. Theparameters used for simulation are given in Table 5.

In the simulation, the time is divided in reservation periods, eachreservation period contains an S-Aloha part, a broadcast channel partand a transmission window. This is shown in FIG. 28. In this system,collisions might occur in the S-Aloha part. In the simulation, theallocation scheme follows the First In First Out (FIFO) rule. However,fair scheduling algorithms should be considered in real implementations.If the request is received by the AP, the user will not resend therequest, unless there is a change in the user's buffer. The requestremains in the AP “request queue”.

The time of each slot in the slotted Aloha includes SIFs+transmissiontime of request packet of size 50 bytes.

TABLE 5 Parameter Value Number of Users Variable Application Data RateVariable PER (Data Packet) 0 PER (ACK) 0 PER (S-Aloha Packet) 0 MAC PDUSize (bytes) 1500 MAC Header Size (bytes) 50 Request Packet Size(slotted 50 Aloha) (bytes) ACK Size (bytes) 30 ACK Transmission Rate 54(Mbps) Data Transmission Rate 120 (Mbps) Physical Layer Preamble (us) 20Maximum Number of 4 Retransmissions PER (Data Packet) 0 PER (ACK) 0 PER(S-Aloha Packet) 0 SIFS (us) 10 DIFS (us) 34 Minimum Contention Window16 (for IEEE 802.11e) (slots) 10 (for S-Aloha) Maximum Contention Window256 (for IEEE (slots) 802. lie) 40 (for S-Aloha) TransmissionOpportunity 1 or 3 Slot Size (us) 9 (for IEEE 802.11e) 14.81 (forS-Aloha) Number of Slots 10 Reservation Period (ms) 7 ReservationTransmission 54 Rate (Mbps) Broadcast Information (bytes) 550 BroadcastData Rate (Mbps) 54 % of Hidden Node 0, 10, 20

The goal of the simulations delay is to determine the average throughputfor a given acceptable delay and the average transmission delay for allusers in the system. The delay is determined defined as the differencebetween the time the packet is successfully received by the AP and thetime the packet arrived at the user's buffer. The average delay isdetermined for all the packets transmitted from all users. Thethroughput is defined as the total number of bits successfullytransmitted over the entire simulation divided by the total simulationtime. The total simulation time for all our simulations wasapproximately 150 seconds.

In the simulation, it is assumed that an application data rate is 2 Mbpsfor each user and the delay and the throughput were determined fordifferent number of users in the system. It is also assumed that thepacket error rate to be zero. The curves for throughput and averagedelay are shown in FIGS. 29 and 30, respectively. As the number of usersin the system increases, the delay increases until the system becomesunstable. When the queue starts building up, the delay starts growingexponentially, and the system becomes unstable. The delay curve showsthe maximum number of users that can be supported before the systembecome unstable (the delay values for unstable system are not meaningfuland not shown). For the MAC of the present invention, total of 32 userseach at 2 Mbps is supported. For an IEEE 802.11e system without hiddennodes, the users supported are 22 and 28 for number ofpackets/transmission opportunity equal to 1 and 3, respectively. For anIEEE 802.11e system with 10% hidden links, the users supported are 18and 22 for transmission opportunity equal to 1 and 3.

Considering all overhead in the system (i.e., inter-frame spacing,headers, preambles and acknowledgments), the maximum achievablethroughput is 55% of the offered bandwidth, which is approximately 66Mbps (for an assumed physical layer raw data rate average of 120 Mbps).With 32 users, the throughput is approximately 64 Mbps, which is closeto the maximum achievable. The only limitation in the present inventionis the available bandwidth limitation.

However, in an IEEE 802.11e system, the limitation is not only due tothe bandwidth limitation, but also because of collisions, especially inthe case where there are hidden nodes. As the probability of hiddennodes increases, the system capacity decreases. For 10% hidden links,IEEE 802.11e supports 44 Mbps. This means that the present inventionprovides 60% gain in throughput (from 40 Mbps to 64 Mbps) over IEEE802.11e.

The gain comes with a penalty of a small increased delay. One of thecauses of the increase in delay is that the users need to wait anaverage of 3.5 ms in order to send a request for bandwidth to the AP(since the reservation period is equal to 7 ms). However, these delaysare in the order of few tens of millisecond to a maximum of 100millisecond depending on the offered load. This is not a significantdelay for NRT services running as background for best effort traffic.

System Capacity (in Terms of Average User Throughput).

After fixing the number of users and varying the application data rateof each user, the objective is to find out, for a given number of usersin the system, what the maximum supported data rate per user is. Thepercentage of hidden links is assumed to be 10%, 20% or 30%. Thetransmission opportunity is equal to 3 in all cases. The results for 8users are shown in FIGS. 31 and 32.

For 8 users, the present invention can support 8.2 Mbps application rateper user. For an IEEE 802.11e system, the maximum data rate that can besupported is 6.3 Mbps, 5.5 Mbps and 5.2 Mbps per user for the case of10%, 20% and 30% hidden links, respectively.

Similar simulation was done for 12 users. The present invention cansupport 5.4 Mbps application rate per user. For an IEEE 802.11e system,the maximum data rate that can be supported is 4.1 Mbps, 3.6 Mbps and3.3 Mbps for each user for the case of 10%, 20% and 30% hidden links,respectively. There is a small penalty in delay in order to get thesehigher data rates. An improvement in throughput is 31% to 58% for 8users and 31% to 64% for 12 users.

The present invention provides guaranteed QOS for RT services. IEEE802.11e can support RT services on EDCA or HCCA mode. In EDCA, RTservices get higher priority than background and best effort (mainly NRTservices) but no guaranteed QoS. AP and STA both contend for resources.However, AP has slightly higher priority than STA. The RT services onEDCA service have similar performance numbers as shown above. In HCCA,RT services are setup by polling the STA at certain interval based onthe QOS negotiation during setup. HCCA can provide guaranteed QOS, but,it needs to send a poll packet to initiate uplink packet transfer. STAneeds to respond back with a data packet or IEEE 802.11ACk packet withina SIFs time. Also, the STAs need to listen continuously even to sendsome information once every 100 millisecond (such as video on Demand).The present invention not only provides guaranteed QOS, but, also doesnot require STA to be awake all the time. The STA supporting only RTservice can save battery by an amount that depends on the characteristicof the application. (STA only need to be awake to listen for extendedbeacon and/or SRA. The present invention is approximately 10% to 25%more efficient in uplink for low data rate high latency application(such as VoIP) as it does not require a poll packet for every uplinktransfer IEEE 802.11e MAC may become less efficient if the STA AMC isunable to send the data packet in response to a poll within a SIFsperiod. This imposes a stringent requirement on the AMC turn around timewhich cannot happen in our MAC, STAs are aware of the scheduledtransmissions and/or reception at the beginning of the superframe.

The present invention is also applicable to peer-to-peer communication.In general, STAs are not allowed to transmit frames directly to otherSTAs in a BSS and should always rely on the AP for the delivery of theframes. However, STAs with QoS facility (QSTAs) may transmit framesdirectly to another QSTA by setting up such data transfer using DirectLink Protocol (DLP). The need for this protocol is motivated by the factthat the intended recipient may be in power save mode, in which case itcan only be woken up by the QAP. The second feature of DLP is toexchange rate set and other information between the sender and thereceiver. Finally, DLP messages can be used to attach securityinformation elements.

Messaging procedure to setup DLP is explained. FIG. 33 is a blockdiagram of DLP signaling. The message exchange to start DLP between twoQSTAs 3305, 3310 follows the following fours steps:

-   -   1.) A station 3305 that intends to exchange frames directly with        another non-AP station 3310, invokes DLP and sends a DLP Request        frame 3320A to an AP 3315. This request contains the rate set,        and capabilities of QSTA 3305, as well as the MAC addresses of        the QSTAs 3305, 3310.    -   2.) If the QSTA 3310 is associated in the BSS, direct streams        are allowed in the policy of the BSS and the QSTA 3310, the AP        3310 forwards the DLP request 3320B to the recipient, STA 3310.    -   3.) If STA 3310 accepts direct streams, it sends a DLP-response        frame 3325A to the AP 3315, which contains the rate set,        (extended) capabilities of the QSTA 3310 and the MAC addresses        of the STAs 3305, 3310.    -   4.) The AP 3315 forwards the DLP-response 3325B to the QSTA        3305, after which the direct link is established.

DLP teardown can be initiated by either of the two QSTAs 3305, 3310. Itcannot be initiated by the QAP 3315. The QSTAs 3305, 3310 can teardownDLP due to expiry of inactivity time expiry or completion of theapplication. Each QSTA 3305, 3310 restarts a timer after every packetreception (data or ACK) from the other QSTA 3305, 3310. If there are nopackets received within the timer expiry, the QSTA 3305, 3310 will sendthe message to the QAP 3315 for DLP teardown. All the packets henceforthshould be sent through the QAP 3315.

Both of the QSTAs 3305, 3310 may use Direct Link for data transfersusing any of the access mechanisms defined in the standard. The QSTAs3305, 3310 may also set up Block ACK if needed. If needed, the QSTAs3305, 3310 may set up traffic streams with the HC to ensure they haveenough bandwidth or use polled transmit opportunities (TXOPs) for datatransfer. A protective mechanism (such as transmitting using HCCA, usingRTS/CTS or the mechanism described in 9.13 of the IEEE 802.11e standard)should be used to reduce the probability of other stations interferingwith the direct link transmissions.

The QSTA 3305 uses following steps to get polled while DLP is setup withanother QSTA 3310. After the completion of DLP setup (defined inprevious paragraphs), the QSTA 3305 negotiates with the QAP 3315 (HC,hybrid coordinator) to gain TXOP that it will use to send the data.There is no negotiation between QSTA 3305 and the QSTA 3310 regardingcapabilities during this period. This time is solely negotiated by theQSTA 3305 and the QAP 3315. The QOS Action frame is used by the QSTA3305 to send the request for traffic stream (i.e. time) and QOS Actionframe is used by the QAP 3315 to respond back to the request. It isassumed that the traffic class is setup after DLP setup as it is logicalway of negotiating BW once the two STAs have exchanged capabilities.

The QAP 3315 polls the QSTA 3305 after a certain interval based on thenegotiated mean data rate and maximum service interval. The QSTA 3305uses this TXOP to transmit and receive packet from the QSTA 3310.However, the QSTA 3305 sends the first packet to ACK the poll from QAP3315. It then sends the packets to the QSTA 3310 which may respond backwith a DATA+ACK packet. There can be more than one data transfer everyTXOP.

After the DLP setup, the QSTAs 3305 and 3310 may negotiate certain BWbased on EDCA rules. QOS Action frame is used for negotiation. EDCAchanges the priority of different traffic class by changing the back-offwindow and Inter frame spacing (IFS). The negotiation decides the amountof time allowed over a certain period. The QSTAs 3305, 3310 may have toself police itself for higher priority traffic (i.e. setting of backoffwindow and IFS). However, the QAP 3315 or the QSTAs 3305, 3310 areallowed to send the packets (of high priority traffic) under lowestpriority settings if they need. The QSTA 3305 and/or the QSTA 3310 cansend data packets to each other directly based on the negotiated EDCAparameters.

The present invention sets forth the signaling required for efficientpeer-to-peer communication in Ad hoc Mode, and includes improvements inthe current Peer-to-Peer Communication to take advantage of the channelcharacteristic and providing RRM control to the AP (Infrastructuremode).

Each device maintains a database of all the devices within a hop and twohops. One hop devices are the ones that can hear, (i.e., receive signalsfrom) each other, (hereinafter “neighbors”). Two hop devices are the onethat are not heard directly. But, a neighbor can hear it.

The neighbor devices can also send signals between each other to informcapabilities. These signals can be part of an initialization process,(when the device is powered on). It can be periodic or event triggeredby some activity or inactivity of any device. These signals can also bea reply to an information request signal initiated by one of thedevices.

Before running an application between two devices, one or both thedevices inform the neighbor about the application. This information canbe sent as a broadcast and/or propagated to the second level neighbors.It can be a directed packet only between the transmitter and thereceiver. There are two groups of devices that need to be told the mediais in use: the ones that can hear the transmission and the ones thatcould possibly transmit and interfere with the reception. Therefore,only the transmitting device and the receiving device need to informtheir neighbor devices. The transmitting device needs to tell itsneighbors that the medium is in use and they cannot receive withoutinterference. The receiving device needs to tell its neighbors that themedium is in use and that they should not transmit. This may requiresome handshaking, but it will yield better overall medium efficacy.

Possible information that can be communicated between devices include,but are not limited to, BW requirement, transmitter or receiver,frequency band, preferred modulation mode, subcarriers, MIMO enabled andcode, or the like.

This information may be sent again on the request of another device.This device can ask for this information to update its statistics or tostart a new application. New Device sends a broadcast message to theneighbors asking for active transmission. The device can passively scanthe channels and then send directed packets as well. Upon reception ofthe request, any device in active section sends the information back tothe new device. The devices follow a random back off before responding.

Once the new device gets this information it can decide to use thisinformation to optimally allocate resources for starting the newapplication. Some services/applications will have priority over others.These services will disrupt other services (if required). An example ofthis service is VoIP for 911 calls.

The disruption can be done by message exchange between othertransmitting nodes to stop their service; and message exchange tore-negotiate the bandwidth, sub carrier, frequency band, or the like.

The present invention introduces the following steps shown in FIG. 34:

Discovery of the QSTA 3310 MAC by the QSTA 3305 (optional): If the QSTA3305 wants to search for the QSTA 3310, it sends a message to the QAP3315 (a message similar to Action Frame). If the QAP 3315 is aware ofthe QSTA 3310, it responds back with the relevant MAC information to theQSTA 3305. Otherwise, the QAP 3315 sends a failure message. This is donebefore DLP setup.

Message 1 a: The QSTA 3305 sends optimal PHY rate and/or other channelquality information between itself and the QSTA 3310 in the DLP RequestPacket. This information may be obtained from previous transmissionsbetween the two QSTAs 3305, 3310, or by listening to the transmissionsfrom QSTA 3310 (to the QAP 3315 or other QSTAs). If the information isnot available, the QSTA 3305 sends the DLP Request Packet with this IEset to NULL.

Message 3320B and 3325A: Not Changed.

Message 3325B: The QAP 3315 may decide whether or not to support DLP forthe QSTAs 3305, 3310 based on the channel quality between the two QSTAs3305, 3310. If the QAP 3315 decides not to support the two QSTAs 3305,3310 with DLP, the QAP 3315 rejects the DLP request on the grounds ofinadequate channel quality (not part of messaging in the currentstandard).

Messages 3400A and 3400B (optional): The QAP 3315 may decide to send aDLP Packet for request on channel quality measurement to the QSTA 3305(message 3400A). The QAP 3315 sends the information on the capability ofthe QSTA 3310 to the QSTA 3305. The QSTA 3305 responds back to the QAP3315 with the channel quality measurement between the two QSTAs 3305,3310 (message 3400B). The message 3400A and 3400B may occur before themessage 3325B or during an ongoing DLP session. This will be useful toget the MIMO capability information before even the DLP setup.

Messages 3400A and 3400B are optional and will only be recognized andused for STAs and APs which support this added capability. STAs and APscompatible with only IEEE 802.11e DLP will not support messages 3400Aand 3400B.

The QAP 3315 is allowed to tear down the DLP. The DLP response messageis modified to allow tear down by the QAP 3315. The DLP tear downmessage should contain a timer after which the QSTA 3305 should send atear down message to the QAP 3315. It allows complete backwardcompatibility. A QSTA that does not recognize DLP tear down message canignore it. This can be in any access method (assigned resourceallocation, management resource allocation, HCCS or EDCF).

It is the responsibility of QSTA 3305 or the QSTA 3310 to negotiate thetraffic stream (i.e. resource allocation in our case). If a QSTA wantsto use EDCA or HCCA, it follows the procedures defined in backgroundsection. In the present invention, data transfer has following steps:

The QSTA 3305 sends the request packet in the open MRAs. Open MRAs arecontention periods for BW request by the associated STAs. The resourceallocation information is sent in the broadcast following the open MRA.The Request and Response IE needs to modify to specify peer-to-peercommunication and addition of the MAC address of the QSTA 3310.

Resource Allocation. It is the responsibility of the QSTA 3305, 3310 todefine the QOS requirement of the application and request the BWaccordingly. The QAP 3315 responds back with the BW allocationinformation. Typically, an RT application has resources allocated overthe duration of application, whereas, an NRT application gets resourcesassigned on the need basis. Resource is allocated by the QAP 3315.

For an RT application, this information is broadcast in every EB. The IEcontains the STA IDs of both the QSTA 3305 and the QSTA 3310. This isneeded to ensure that both of the QSTAs 3305, 3310 are awake during theassigned time.

At the assigned time and/or channel, the QSTA 3305 sends the firstpacket to the QSTA 3310. The QSTA 3310 can respond back with the ACK orData+ACK as negotiated between the two STAs 3305, 3310.

For NRT application, the steps are very similar. However, the QAP 3315assigns the resource after the open MRA period is over via Resourceallocation message (broadcast message). It is only assigned for a shortduration to satisfy the current buffer occupancy requirement. The firstpacket is sent by the QSTA 3305.

A QSTA, that has background services supported over a DLP session, needsto listen to the broadcast message after the open MRAs. A QSTA, that hasstreaming and/or RT services supported over DLP, needs to listen for EB.The QSTA is expected to be awake in the scheduled transmissions time.

For support of channel estimation and information before or during DLPsetup (optional), the QSTA 3305 can send a request packet to the QAP3315 in an open MRA. The QAP 3315 may assign a MRA for the two QSTAs3305, 3310 to communicate with each other. This information is sent inthe next EB period. The measurement information is sent back to the QAP3315 by the QSTA 3305 during the assigned MRA.

The QSTA 3305 can also send a packet directly to the QSTA 3310 in anopen MRA with a CSMA/CA access mechanism. The QSTA 3305 can send thisinformation in an open MRA. The measurement packets support themechanism to get information on channel quality (CQI) and state (CSI).

In IEEE 802.11e, the QSTA 3305 sends the measurement packet to the QSTA3310 in an EDCA and then informs the QAP 3315 about channel quality.There is no need for additional messaging to support MIMO between twoQSTAs 3305, 3310 during data transfer (specifically for DLP). Thechannel feedback to improve MIMO data rate or PER during QAP to QSTAcommunication is similar to STA to STA.

Several Action frame formats are defined for DLP Management purposes. AnAction field, in the octet field immediately after the Category field,differentiates the formats. The Action field values, associated witheach frame format are defined in Table 6.

TABLE 6 Action Field Value Meaning 0 DLP request 1 DLP response 2 DLPteardown 3-255 Reserved

The following Action field Values are added.

DLP Discovery Request: QSTA sends the packet to AP to get the MACaddress of the device by sending application requirements.

DLP Discovery Response: AP responds back with MAC address of the device.

DLP Teardown (modified): Action field is added for DLP Teardown by theAP. The frame has information filed called timer. AP expects that QSTAsends the DLP teardown message to QAP within that time.

DLP Request (modified): Additional element to send optimal PHY data rateand certain other channel characteristic between the two STAs.

DLP Measurement Request: action item value is added for DLP MeasurementRequest from the QAP 3315 to the QSTA 3305. It contains the capabilityinformation of the QSTA 3310.

DLP Measurement Response: action item value is added for DLP MeasurementResponse from the QSTA 3305 to the QAP 3315. It contains measurementinformation and the MAC address of the QSTA 3310.

BW Request Packet which contains following information: The QSTA 3310MAC address, P2P Option, Optimal PHY data rate, BW Response Element, andalternative method of performing DLP with centralized controller.

Each device maintains a database of all the devices with which it candirectly communicate and also which devices it can communicate withthough an AP. The AP can provide the database of available devicesavailable through the AP.

Each node is connected to the AP. However, all the traffic does notnecessarily originate from and to the AP. In this case, the two nodescan talk to each other directly without sending the traffic through AP.There are basically two ways to control this process: AP control anddistributed control similar to the non-AP case above.

Using AP control this can be done by using some or all the followingsteps:

Node1 sends a message to the AP with destination id, BW required,Channel information, direct hop to the destination or the like. The APbased on the received information can decide to let the two STAs talk toeach other directly or through the AP. It can be based on the signalstrength between the two nodes, current network load, AP activity,capability of the two nodes, or the like. The AP can decide to assignresources, (e.g., a certain time, sub-carriers or antennas for thisconnection), based on the requirement and what is available. Thisinformation is sent to both the Node1 and Node2 and could be sent asdirected packet. Other nodes are informed so that they are aware theresource is in use. They can be informed by broadcast to all the nodesor by requiring all nodes to monitor AP allocation information (even ifit is not intended for their use). This prevents other nodes from usingthe same resources.

In wireless LANs the access to the medium is typically distributed.However, the AP has higher priority than non-AP STA. So the AP cantherefore grab the wireless medium to administer management functions toregulate the usage and access of the wireless medium by the STAs. In thepresent invention, the AP grabs the wireless medium after a definedinterval (e.g., DIFS in IEEE 802.11e WLAN standard) and transmits abroadcast message to all STAs indicating that a specified managementresource allocation period (MRAP) shall follow for data packet exchangesand request/reservation for polled transmissions. During the MRAP aslotted Aloha mechanism provides access to the wireless medium.

In the broadcast message from the AP for MRAP, the MRAP parameters suchas type, location and duration and the slotted Aloha parameters shall beincluded. The type could differentiate between MRAPs used for associatedand un-associated STAs.

MRAPs allow associated and unassociated STAs and AP to exchange messagesin a contention mode. The data exchange is typically small data packets,resource allocation requests for polled transmissions,association/reassociation requests

The access mechanism for an MRAP is a slotted Aloha mechanism. In theslotted Aloha mechanism STAs access the wireless medium with short datapackets (small data packets, resource allocation requests,association/reassociation requests). The wireless medium is divided intoslots of size equal to the data packet duration and transmissions areallowed only at the beginning of the slots.

An exponential backoff mechanism is implemented as follows: A back offcounter is maintained at each STA and is decremented every slot. Apending packet is transmitted when the back off counter becomes zero.The back off counter is chosen as a uniformly distributed randomvariable from a contention window. In the first attempt the contentionwindow is set to a minimum contention window. The size of the contentionwindow grows with the number of retransmission attempts until it reachesan upper limit. The rate at which the contention window grows may alsooptionally depend on the priority of the traffic. For example thesmaller the access delay specification of the traffic the slower thegrowth of contention window. Controlling the contention window based onthe access delay specification allows better management of access delaysin a slotted Aloha access under high load situations.

There are two possible methods for the AP to send acknowledgements(ACKs) to the transmissions from STAs in the reservation slots. In onemethod, a collective ACK frame 3505 is sent at the end of the MRAP asshown in FIG. 35. This collective (or aggregated) ACK include individualACKs for all STAs that contented in the MRAP. In another method, atransmission from an STA in the reservation slot is immediately ACKed bythe AP within the same slot as shown in FIG. 36. This method has todefine the slot size to accommodate both the data packet from the STA aswell as the ACK.

The responses to the STAs from the AP follow later in a pollingmechanism administered by the AP. The poll from the AP would haveresource allocation responses for associated STAs that successfullytransmitted their resource allocation requests. It would have theassociation/reassociation responses for unassociated STAs thatsuccessfully transmitted their association/reassociation requests. TheSTAs that were unsuccessful have to retransmit their packets using theback off counter. The backoff counter is decremented only during MRAPs.

In the IEEE 802.11n period, guard times are needed to preventtransmissions in any two adjacent scheduled resource allocations (SRAsor MSRAs) from colliding. The guard time required depends upon thephysical size of the BSS, the drift of the local STA time and the idealtime at the RC. The clock at the STA may be fast or slow relative to theideal time. The propagation delay may have an insignificant impactespecially for distances of suggested in IEEE 802.11n model scenarios.The RC may estimate a single worst case guard time for the entire IEEE802.11n period or between two schedule announcements via the EBs. The RCmay also calculate guard time based on the nature of SRA assignment(quasi-static or dynamic) and the position of the SRA or MSRA in thesuperframe. For example, the quasi-static SRA assignments may requirelonger guard time to keep allocations over superframes the same whileaccommodating small drifts in beacon times.

Admission control may be necessary to efficiently utilize the availablebandwidth resources. Admission control may also be required to guaranteeQoS. The RC can either implement admission control in the network ordefer such admission control decisions to another entity. Admissioncontrol may be standardized by IEEE 802.11n or other groups or may beleft for vendor-implementation of the scheduler. The admission controlmay depend on available channel capacity, link conditions,retransmission limits, and the QoS requirements of a given trafficstream. Any stream may be admitted or rejected based on all of thesecriteria.

FIG. 37 is a flow diagram of a process 3700 for implementing an SRAassignment in a system including at least one STA 3705 and at least oneAP 3710 in accordance with the present invention. The STA 3705 obtainssynchronization and association with the AP 3710 (step 3712). The AP3710 broadcasts an EB which has information for the IEEE 802.11n STAsabout the allocations in IEEE 802.11n period such as SRAs and MSRAs(step 3714).

If legacy operation is enabled, the AP 3710 begins the superframe bytransmitting the legacy beacon. In the legacy beacon, the AP announcesthe CFP thereby preventing legacy STAs from transmitting during thatperiod. If legacy operation is not supported the beacon need not exist.

When the STA 3705 wants SRA resources at step 3716, the STA 3705 readsEB to locate MSRA (step 3718). The STA 3705 chooses an MSRA to send aresource allocation request via a slotted Aloha mechanism (step 3720).The STA 3705 sends a resource allocation request to the AP 3710 (step3722). The AP 3710 receives the request and assigns an SRA (step 3724).The AP 3710 then sends an acknowledgement to the STA, (individually orcollectively) (step 3726). The AP 3710 then broadcasts an EB whichcontains the information for the SRA assignment (step 3728). The STA3705 reads the EB and knows which SRA is assigned to it (step 3730). TheSTA 3705 may optionally enter a standby mode until the SRA is assigned(step 3732). The STA 3705 reenters to an active mode upon the assignedSRA beginning (step 3734) as the AP 3710 awaits for activity of the STA3705 (step 3736). Data is transmitted on the assigned SRA (step 3738).If the STA 3705 completes the operation prior to end of the assigned SRA(step 3740), the STA 3705 sends an end of transmission indicator to theAP 3710 (steps 3742). If the AP 3710 receives an end of transmissionindicator or no activity detected within DIFS, the AP 3710 reclaims theSRA resources (step 3744). The STA 3705 may enter a standby mode until anext SRA location is read from the EB (step 3746).

FIG. 38 shows a wireless communication system 3800 for controllingaccess to a wireless communication medium. The system 3800 includes anAP 3805 and at least one STA 3810.

The AP 3805 includes a processor 3815, a receiver 3820 and a transmitter3825. The processor 3815 is capable of defining a superframe fortransmission of data in time domain, the superframe including an HTperiod which includes at least one SRA and at least one MSRA. The SRA isdefined for transmitting traffic data between the AP 3805 and the STA3810, and the MSRA is defined for transmitting management and controldata between the AP 3805 and the STA 3810. The transmitter 3825 iscoupled to the processor 3815 for broadcasting an EB. The EB includesinformation about the SRA and MSRA. The receiver 3820 is also coupled tothe processor 3815 for receiving a resource allocation request (RAR)from a STA. The transmitter 3825 sends a response to the RAR forallocating at least one of a particular SRA and an MSRA for the STA3810.

The STA 3810 includes a processor 3830, a receiver 3835 and atransmitter 3840. The receiver 3835 is coupled to the processor 3830 andreceives the EB. The transmitter 3840 is also coupled to the processor3830 and sends an RAR to the AP 3805 in an MSRA when the STA 3820 needsto access the medium for transmitting traffic data, whereby the STA 3810and the AP 3805 transmit data at the allocated SRA.

Although the features and elements of the present invention aredescribed in the preferred embodiments in particular combinations, eachfeature or element can be used alone without the other features andelements of the preferred embodiments or in various combinations with orwithout other features and elements of the present invention.

What is claimed is:
 1. A method for use in an Institute of Electricaland Electronics Engineers (IEEE) 802.11n access point (AP), the methodcomprising: broadcasting, by the IEEE 802.11n AP, an IEEE 802.11 legacybeacon in a beacon interval, wherein the IEEE 802.11 legacy beacon isdecodable by legacy IEEE 802.11 stations (STA)s and IEEE 802.11n STAsand includes an indication of whether a second beacon will bebroadcasted by the IEEE 802.11n AP within the beacon interval; andbroadcasting, by the IEEE 802.11n AP, the second beacon in the beaconinterval, wherein the second beacon is an IEEE 802.11n beacon that isdecodable only by IEEE 802.11n STAs.
 2. The method of claim 1, whereinthe indication of whether a second beacon will be broadcasted by theIEEE 802.11n AP within the beacon interval indicates when the IEEE802.11n beacon will be broadcasted by the IEEE 802.11n AP within thebeacon interval.
 3. The method of claim 1, wherein the IEEE 802.11nbeacon includes information included in the IEEE 802.11 legacy beacon.4. The method of claim 1, wherein the IEEE 802.11n beacon is identicalto the IEEE 802.11 legacy beacon.
 5. The method of claim 1, wherein theIEEE 802.11n beacon includes an identification of the IEEE 802.11nbeacon.
 6. The method of claim 1, wherein the beacon interval is a timeperiod between successive broadcasts of the IEEE 802.11 legacy beacon bythe AP.
 7. The method of claim 1, wherein the IEEE 802.11n beaconcomprises an information element (IE) that indicates a plurality ofsupported rates.
 8. The method of claim 1, wherein the IEEE 802.11nbeacon comprises an information element (IE) that indicates anorthogonal frequency division multiplex (OFDM) multiple input multipleoutput (MIMO) parameter set.
 9. The method of claim 1, wherein the IEEE802.11n beacon comprises an information element that indicates channelinformation.
 10. The method of claim 1, wherein the indication ofwhether a second beacon will be broadcasted by the IEEE 802.11n APwithin the beacon interval includes one of a periodicity, frequencyband, or subchannel information of the second beacon.
 11. The method ofclaim 1, wherein the IEEE 802.11n beacon has a greater transmissionrange compared to the IEEE 802.11 legacy beacon.
 12. The method of claim1, wherein the IEEE 802.11n beacon includes an indication that the IEEE802.11n beacon is an IEEE 802.11n beacon.
 13. An Institute of Electricaland Electronics Engineers (IEEE) 802.11n access point (AP) comprising: atransmitter configured to: broadcast an IEEE 802.11 legacy beacon in abeacon interval, wherein the IEEE 802.11 legacy beacon is decodable bylegacy IEEE 802.11 stations (STA)s and IEEE 802.11n STAs and includes anindication of whether a second beacon will be broadcasted by the IEEE802.11n AP within the beacon interval; and broadcast the second beaconin the beacon interval, wherein the second beacon is an IEEE 802.11nbeacon that is decodable only by IEEE 802.11n STAs, and wherein the IEEE802.11n beacon includes an indication that the IEEE 802.11n beacon is anIEEE 802.11n beacon.
 14. The IEEE 802.11n AP of claim 13, wherein theindication indicates when the IEEE 802.11n beacon will be broadcasted bythe IEEE 802.11n AP within the beacon interval.
 15. The IEEE 802.11n APof claim 13, wherein the transmitter is configured to broadcast an IEEE802.11n beacon that includes information included in the IEEE 802.11legacy beacon.
 16. The IEEE 802.11n AP of claim 13, wherein thetransmitter is configured to broadcast an IEEE 802.11n beacon that isidentical to the IEEE 802.11 legacy beacon.
 17. The IEEE 802.11n AP ofclaim 13, wherein the transmitter is configured to broadcast an IEEE802.11n beacon that includes an identification of the IEEE 802.11nbeacon.
 18. The IEEE 802.11n AP of claim 13, wherein the beacon intervalis a time period between successive broadcasts of the IEEE 802.11 legacybeacon.
 19. The IEEE 802.11n AP of claim 13, wherein the transmitter isconfigured to broadcast an IEEE 802.11n beacon that comprises aninformation element (IE) that indicates a plurality of supported rates.20. The IEEE 802.11n AP of claim 13, wherein the transmitter isconfigured to broadcast an IEEE 802.11n beacon that comprises aninformation element (IE) that indicates an orthogonal frequency divisionmultiplex (OFDM) multiple input multiple output (MIMO) parameter set.21. The IEEE 802.11n AP of claim 13, wherein the transmitter isconfigured to broadcast an IEEE 802.11n beacon that comprises aninformation element (IE) that indicates channel information.
 22. TheIEEE 802.11n AP of claim 13, wherein the transmitter is configured tobroadcast an IEEE 802.11n beacon that has a greater transmission rangecompared to the IEEE 802.11 legacy beacon.
 23. The IEEE 802.11n AP ofclaim 13, wherein the indication of whether a second beacon will bebroadcasted by the IEEE 802.11n AP within the beacon interval includesone of a periodicity, frequency band, or subchannel information of thesecond beacon.
 24. A method for use in an Institute of Electrical andElectronics Engineers (IEEE) 802.11n high throughput (HT) station (STA),the method comprising: receiving, from an IEEE 802.11n access point(AP), an IEEE 802.11 legacy beacon in a beacon interval, wherein theIEEE 802.11 legacy beacon is decodable by legacy IEEE 802.11 STAs andIEEE 802.11n STAs and includes an indication of whether a second beaconwill be received from the IEEE 802.11n AP within the beacon interval;and receiving, from the IEEE 802.11n AP, an IEEE 802.11n beacon in thebeacon interval, wherein the IEEE 802.11n beacon is decodable only byIEEE 802.11n STAs.
 25. The method of claim 24, wherein the indication ofwhether the second beacon will be received from the IEEE 802.11n APwithin the beacon interval indicates when the IEEE 802.11n beacon willbe received within the beacon interval.
 26. The method of claim 24,wherein the IEEE 802.11n beacon includes information included in theIEEE 802.11 legacy beacon.
 27. The method of claim 24, wherein the IEEE802.11n beacon is identical to the IEEE 802.11 legacy beacon.
 28. Themethod of claim 24, wherein the IEEE 802.11n beacon includes anidentification of the IEEE 802.11n beacon.
 29. The method of claim 24,wherein the beacon interval is a time period between successivebroadcasts of the IEEE 802.11 legacy beacon from the IEEE 802.11n AP.30. The method of claim 24, wherein the IEEE 802.11n beacon comprises aninformation element (IE) that indicates a plurality of supported rates.31. The method of claim 24, wherein the IEEE 802.11n beacon comprises aninformation element (IE) that indicates an orthogonal frequency divisionmultiplex (OFDM) multiple input multiple output (MIMO) parameter set.32. The method of claim 24, wherein the IEEE 802.11n beacon comprises aninformation element (IE) that indicates channel information.
 33. Themethod of claim 24, wherein the IEEE 802.11n beacon has a greatertransmission range compared to the IEEE 802.11 legacy beacon.
 34. Themethod of claim 24, wherein the IEEE 802.11n beacon includes anindication that the IEEE 802.11n beacon is an IEEE 802.11n beacon. 35.The method of claim 24, wherein the indication of whether a secondbeacon will be broadcasted by the IEEE 802.11n AP within the beaconinterval includes one of a periodicity, frequency band, or subchannelinformation of the second beacon.
 36. An Institute of Electrical andElectronics Engineers (IEEE) 802.11n high throughput (HT) station (STA)comprising: a receiver configured to: receive, from an IEEE 802.11naccess point (AP), an IEEE 802.11 legacy beacon in a beacon interval,wherein the IEEE 802.11 legacy beacon is decodable by legacy IEEE 802.11STAs and IEEE 802.11n STAs and includes an indication of whether asecond beacon will be received from the IEEE 802.11n AP within thebeacon interval; and receive, from the IEEE 802.11n AP, the secondbeacon in the beacon interval, wherein the second beacon is an IEEE802.11n beacon that is decodable only by IEEE 802.11n STAs.
 37. The IEEE802.11n HT STA of claim 36, wherein the receiver is further configuredto receive an indication that includes when the IEEE 802.11n beacon willbe received from the IEEE 802.11n AP within the beacon interval.
 38. TheIEEE 802.11n HT STA of claim 36, wherein the receiver is configured toreceive an IEEE 802.11n beacon that includes information included in theIEEE 802.11 legacy beacon.
 39. The IEEE 802.11n HT STA of claim 36,wherein the receiver is configured to receive an IEEE 802.11n beaconthat is identical to the IEEE 802.11 legacy beacon.
 40. The IEEE 802.11nHT STA of claim 36, wherein the receiver is configured to receive anIEEE 802.11n beacon that includes an identification of the IEEE 802.11nbeacon.
 41. The IEEE 802.11n HT STA of claim 36, wherein the beaconinterval is a time period between successive broadcasts of the IEEE802.11 legacy beacon from the IEEE 802.11n AP.
 42. The IEEE 802.11n HTSTA of claim 36, wherein the receiver is configured to receive an IEEE802.11n beacon that comprises an information element (IE) that indicatesa plurality of supported rates.
 43. The IEEE 802.11n HT STA of claim 36,wherein the receiver is configured to receive an IEEE 802.11n beaconthat comprises an information element (IE) that indicates an orthogonalfrequency division multiplex (OFDM) multiple input multiple output(MIMO) parameter set.
 44. The IEEE 802.11n HT STA of claim 36, whereinthe receiver is configured to receive an IEEE 802.11n beacon thatcomprises an information element (IE) that indicates channelinformation.
 45. The IEEE 802.11n HT STA of claim 36, wherein thereceiver is configured to receive an IEEE 802.11n beacon that has agreater transmission range compared to the IEEE 802.11 legacy beacon.46. The IEEE 802.11n HT STA of claim 36, wherein the receiver isconfigured to receive an IEEE 802.11n beacon that includes an indicationthat the IEEE 802.11n beacon is an IEEE 802.11n beacon.
 47. The IEEE802.11 HT STA of claim 36, wherein the indication of whether a secondbeacon will be broadcasted by the IEEE 802.11n AP within the beaconinterval includes one of a periodicity, frequency band, or subchannelinformation of the second beacon.